Tens of thousands of people have fled Bangkok ahead of a high tide expected to worsen floods that have inundated the Thai capital and killed at least 377 people since mid-July.
Bangkok's Chao Phraya River is expected to burst its banks over the weekend during the unusually high tide that began on Friday, and is expected to reach its peak on Saturday.
Buildings across the capital have been sand-bagged for protection and some vulnerable streets were virtually deserted.
"Thousands of people around Bangkok are leaving because of the flood disaster spreading," Al Jazeera's Wayne Hay reported from the city.
"Some people choosing to leave their homes before the flood waters arrive, others are under compulsory evacuation orders.
"Aiding in the whole evacuation process and the relief and recovery effort, some 50,000 more troops are being deployed around Bangkok to help out as the flood disaster worsens.
"Also, more options are being considered to try and divert as much water as they can around the outskirts of the city to protect the inner part of Bangkok."
The flooding is estimated to have disrupted the lives of nearly 2.2 million people over the past few months.
Thailand has asked a US navy destroyer to extend its stay at a main port to allow American helicopters to survey the deadly floodwaters, the Pentagon said on Friday.
Two SH-60 Seahawk choppers aboard the USS Mustin will will conduct "aerial reconnaissance for the Thai government", Captain John Kirby told reporters.
Al Jazeera's Wayne Hay reports from Bangkok
The ship docked at Laem Chabang a few days ago for a week-long stint but "the destroyer Mustin will be staying in Thailand a little bit longer now," he said.
"The Thai government has asked to have it stick around to help out."
The US navy initially sent an aircraft carrier and other ships to the area for possible assistance with relief efforts, but the Bangkok government never issued a formal request for help and the vessels departed.
The Thai military also had said earlier it did not require assistance from US forces to contend with the flooding, which has gone on for three months, mostly in northern and central Thailand.
The higher-than-normal tides in the Gulf of Thailand are obstructing the flood runoff from the north and there are fears that the overflows could swamp parts of the city centre.
The goverment has expressed concern that major barriers and dikes could break.
Friday morning's high tide - measured at 2.47m above sea level - was lower than expected, however, raising hopes that the Chao Praya's flood barriers would prevent a major overflow.
"The navy predicted 2.57m on Saturday but I think it will be bit lower based on today," an official at the city's drainage and sewerage department who did not want to be named, told the AFP news agency.
"So the walls can still hold it back, despite flooding on the river banks which is usual during high tide."
Seven of Bangkok's 50 districts - all in the northern outskirts - are already heavily flooded.
Residents have fled aboard bamboo rafts and army trucks and by wading in waist-deep water. Provinces north of the capital have been submerged, with factories and homes ruined.
Fears the inner city could flood prompted an exodus this week, as Thais and expatriates alike sought refuge outside Bangkok, and foreign governments urged their citizens to avoid unessential travel to the threatened city.